GAF is a growth factor composed of a heparin-binding polypeptide having a molecular weight of about 30,000 as a whole molecular type, the polypeptide being first separated from glioma cells by purification [K. Naruo et al., J. Biol. Chem., 268, 2857 (1993)]. The amino acid sequence thereof (FIG. 1) has proved that GAF is one member of the family of fibroblast growth factors (hereinafter, "FGFs"). GAF having about 30% homology with each factor of the FGF family in the amino acid sequence is called "FGF9" [M. Miyamoto et al., Mol. Cell. Biol., 13, 4251 (1993)]. The GAF is considered to activate mesodermal cells such as fibroblasts, glial cells and nerve cells. Further, abnormal continuous expression thereof conceivably may lead to the malignant transformation of cells which are reactive to the factor. It is therefore conceivable that an antibody inhibiting GAF's activity can be used as a drug for suppressing progress of diseases such as tumors. The assay of the blood GAF level is also considered to be necessary as one means for diagnosing these diseases. Furthermore, GAF exhibits growth promoting activity upon widely ranging cells including osteoblasts, hepatocites and vascular smooth muscle cells. Accordingly, it is expected that GAF can be widely utilized as a bone formation accelerant, etc. In addition, it has been discovered that GAF acts on megakaryoblasts to promote their growth, thereby increasing the platelets in number. Hence, GAF is also expected to be applied as a platelet-increasing agent.
The assay of the blood GAF level is indispensable for tracing thereof when GAF is administered to, for example, patients with thrombocytopenia.
On the other hand, GAF can be produced by use of host cells such as various microorganisms including Escherichia coli or animal cultured cells, employing recombinant technology, based on the cDNA sequence previously reported, and can be used .similarly with natural extracts. However, GAF has an easily decomposable moiety on the N-terminal side, and contamination with the decomposed product makes it difficult to purify GAF. The region of this easily decomposable moiety has not been determined yet. Further, GAF is not so stable, for example, stability to acids or stability to heat, which results in disadvantages in the application for various drugs.